Carbon fiber reinforced resin moldings produced by impregnating oriented carbon fibers with thermosetting resins, arranging filaments of these fibers unidirectionally to form prepregs, followed by multilayer lamination of these prepregs and molding and curing of resulting laminates are used extensively as industrial materials such as plate springs and honeycomb constructing materials and as sporting or leisure goods such as fishing rods and golf shafts. Recently, those moldings have also been used as members of aircraft, automobiles, ships, and the like.
Performance characteristics of carbon fibers used have also been improved remarkably in recent years; of polyacrylonitrile-based carbon fibers, there have been developed and marketed a high strength, high elongation type having tensile strengths exceeding 600 Kg/mm.sup.2 and a high strength, high elastic modulus type having tensile strengths of at least 300 Kg/mm.sup.2 and tensile elastic moduli of 46-50 ton/mm.sup.2. Performance characteristics required for moldings reinforced with those carbon fibers have been sophisticated more and more against the background of improved performance characteristics of raw material carbon fibers.
The first step of improving the performance of carbon fiber reinforced resin moldings was the enhancement of the adhesive strength between the carbon fiber and the matrix resin. About this matter, extensive researches and developments were made energetically for the past some dozen years and the adhesive strength is settled now on a considerably high level owing to the technique of electrolytic oxidation, the technique of gas-phase oxidation, and some other techniques. Seeing the last several years, however, no marked advance is observed in this art and there is no prospect that properties such as the interlayer shear strength will be improved to large extents in the near future.
While there are already published some reports (Japanese Patent Application Kokai No. Sho. 57-49612, etc.) that a modification of matrix resin contributes to the improvement of its carbon fiber reinforced moldings in performance, not much improvement of the moldings themselves in performance can be expected from the modification of resin when the modified resin has a curing temperature of the same degree. But, matrix resins having higher curing temperatures, higher cross-linking density, and higher stiffness exhibit generally higher interlayer shear strength and higher flexural strength, according to the present inventors' empirical knowledge.